Population dynamics and its driving factors of small yellow croaker (Larimichthys polyactis) in the Yellow and Bohai Seas

Accurate assessment of fishery population dynamics and their driving factors is fundamental to the scientific management of fishery resources. The Yellow and Bohai Seas serve as crucial habitats for numerous fishery organisms, underpinning the sustainable productivity of the ‘maritime granary’ in northern China. The small yellow croaker (Larimichthys polyactis) is an economically important fish species in the Yellow and Bohai Seas, and has long been a primary target for fishing. This study aims to accurately assess the spatio-temporal dynamics of the small yellow croaker population in the Yellow and Bohai Seas, thereby providing a scientific basis for the management of the fishery resources. Based on survey data of small yellow croaker in the Yellow and Bohai Seas and publicly available information from 2001 to 2025, this study employed spatiotemporal modeling and spatial clustering analyses to characterize the spatiotemporal distribution patterns and long–term changes in stock abundance of small yellow croaker. In addition, population dynamics were systematically evaluated using a data–rich stock assessment model, and the driving mechanisms underlying stock fluctuations were further elucidated through structural equation modeling. The results showed that the small yellow croaker mainly overwinters in waters deeper than 50 m, with a small number distributed in the 30–50 m water range and very few in waters shallower than 30 m. In addition to the central and southeastern Yellow Sea, the waters deeper than 50 m in the northern Yellow Sea also serve as an important overwintering ground. The interannual distribution of small yellow croaker population density exhibits significant spatial heterogeneity. In the winter of 2001, small yellow croaker displayed extensive and continuous high-density distribution areas, followed by a decline in resource abundance and contraction of distribution hotspots. By 2025, the center of gravity of the small yellow croaker population had shifted westward, and the distribution hotspots in the central and southern Yellow Sea had achieved a certain degree of recovery. Interannual variability in population density further revealed an uneven and spatially unbalanced recovery across regions. Results from the stock assessment model indicated that the recruitment of small yellow croaker exhibited a high interannual variability. The fishing pressure on this species remained at a low level during 2001–2005, with its stock status in a healthy condition. After 2005, high fishing pressure led to a decline in the spawning stock biomass and impaired recruitment potential. However, with the reduction in fishing pressure in recent years, the population has shown signs of recovery. From 2023 to 2025, the fishing mortality coefficient (F) and spawning potential ratio (SPR) of small yellow croaker performed better than their respective target reference points. Structural equation modeling clearly revealed the dominant drivers of stock dynamics. Fishing pressure is the primary cause of the decline in small yellow croaker resources in the Yellow and Bohai Seas, with its impact far exceeding other factors (path coefficient of F: –1.26). Nevertheless, existing management measures (path coefficient: 0.30) and climatic conditions (path coefficient: 0.27) have supported resource conservation and recovery. The stock recovery of small yellow croaker is constrained by the characteristics of unstable recruitment and spatial imbalance. The impacts of fishing pressure and climatic factors on the stock dynamics of small yellow croaker are often exerted through its spatial distribution pattern. As a non-spatial approach, the stock assessment model used in this study is only capable of characterizing the temporal variations of stock status indicators of small yellow croaker in the Yellow and Bohai Seas, and cannot reflect the spatial differences in stock status. Integrating spatiotemporal distribution patterns with stock status indicators suggests that relying solely on reference points (such as F or SPR thresholds) for management may mask the risk of localized resource decline. Without accounting for the spatial structural characteristics of the small yellow croaker population, the recovery of the overall stock status in recent years indicated by the stock assessment model may mask the differences in recovery among distinct subpopulations, which could potentially lead to inappropriate management adjustments, such as the misallocation of fishing effort. Conducting resource assessments that incorporate spatial dimensions and implementing regionally differentiated resource management are key approaches to maintaining the productivity of small yellow croaker populations in the Yellow and Bohai Seas and enhancing their resource sustainability. This study presents a novel integrated analytical framework that couples spatio-temporal distribution with stock status and their driving factors, which can be extended and applied to the analysis of population dynamics and the formulation of management strategies for exploited fish species in the Yellow and Bohai Seas and even global marine waters.